Systems and methods for optical dark section conditioning

ABSTRACT

Embodiments of the disclosure are directed to optical dark section conditioning. An embodiment generates at least one of a broadband noise or signal at the head end of a section for a first module of the section; and operates all other modules of the section in gain control mode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the disclosure are directed to monitoring dormant orout-of-service fiber optics for layer 0 restoration.

2. Description of the Related Art

Turning up wavelengths in an optical link, especially in a DWDM (densewavelength division multiplexing) system, is becoming time critical interms of layer 0 restoration schemes. Any potential link failures candelay the wavelength turn up and therefore delay or fail the overalllayer 0 restoration with respect to time. Such optical link failuresinclude, but are not limited to, optical line fails, line fiber cut,extended span loss reach in any span that can drive the next amplifierblock, or EDFA (erbium doped fiber amplifier) to shutoff or in inputloss of signal (LOS) state. It is possible to have high back reflectionpresent on the line fiber that could severely impact the performance ofthe optical channels. It can also drive down the amplifier output powerto a lower value by triggering, for example, the amplifier safetymechanisms (e.g., automatic power reduction mechanism or APR). Any ofthe line amplifiers, for example, can be manually set to out-of-servicethat can shutdown the amp causing severe service interruption on thatlink.

If these traffic interrupting link disturbances can be detected ahead oftime for any optical link, that link can be avoided during the phase oflayer 0 restoration. Traffic impacting link disturbances can be detectedwhen links are already carrying some level of traffic channels.

If the link remains dark either in day 1 installation when the link isnot carrying any traffic or after fixing link down related conditions(e.g. fiber cut) where all services were earlier moved due to linkfailures, traffic may be reverted back on the home path after fixing thefault points. If the link is not verified ahead of time, any restorationor reversion action triggered over the dark link may fail due to theabove mentioned link imperfections.

SUMMARY

Embodiments of the disclosure are directed to methods, apparatuses, andnon-transitory computer readable media for optical dark sectionconditioning, including: generating at least one of a broadband noise orsignal at the head end of a section for a first module of the section;and operating all other modules of the section in gain control mode.

Some embodiments may include determining whether a section is dark. Someembodiments may also include closing all per channel actuators at a headend optical add drop multiplexer (OADM) node. Some embodiments mayprovide for closing down pixels in a wavelength selective switch. Theseembodiments may also include moving a per channel or group multiplexervariable optical attenuators to an approximate maximum attenuation.

Some embodiments may include masking an alarm raised by a firstamplifier at the head of the section. In some embodiments, the targetgain for the other modules is based on a span loss of a preceding spanreported by an optical supervisory channel. In some embodiments, thegain for the other modules is substantially based on prior results. Someembodiments include setting gain targets for all modules in gain controlmode. In some embodiments, a section head optical controller waits apredetermined amount of time in order to allow a first amplifier toachieve its output power target prior to setting the other modules inthe section in gain control mode.

Some embodiments may include disabling an automatic shutoff mode for afirst amplifier in a dark section; setting the first amplifier in powercontrol mode; setting an estimated power target to bring a secondamplifier in the section out of shutoff mode, wherein the secondamplifier is the next amplifier in the set after the first amplifier;and setting all remaining amplifiers in the section in gain controlmode.

Some embodiments may include performing optical dark sectionconditioning on more than one dark section. In some embodiments, themore than one dark section comprises at least one of the following: aroute and select based network architecture and a broadcast andselect-based architecture. Some embodiments may include performingoptical dark section conditioning on a section that comprises at leastone Raman amplifier. In some embodiments, at least one of the moduleshas a back-reflector photodiode on an output port to detectback-reflection coming into the port. Some embodiments may include atleast one instruction to reduce output power in order not to damage themodules.

The present embodiments can turn up light in a dark optical sectionbetween two OADMs (optical add drop multiplexers) using system generatednoise that (1) can allow detecting traffic impacting link disturbances,e.g. amplifier shutoff, high back reflections, optical line fail, and(2) can maintain the safety standards and prevent any damaging of theinstalled EDFA base in the DWDM line system. The embodiments can detectlink perturbations without the presence of any traffic carryingchannels, and can help the layer 0 control plane to avoid the faultedoptical link or section ahead of time for any traffic restoration orreversion saving valuable time for restoration. The embodimentsdescribed can also reduce the wavelength turn up time significantly in adark section compared to the conventional way where dark section addtimings are limited by the sequential turn ups and gain settings foreach AMP. The embodiments can use the system's commonly availablephotonic components without introducing any external or additionalphotonic hardware, and can be introduced for any dark optical sectionsin the network remotely without impacting services in any other links.The proposed DSC can allow detecting faults remotely in multipleend-to-end connected fiber spans in parallel while the system is fullyactive, functional and ready to enroll traffic at any point. DSC canalso be applied when the links are not carrying any live traffic. Thecontrol plane can make decisions ahead of time based on DSC data toavoid enrolling traffic on a faulty link until the fault is cleared.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of aspects of the disclosure and many ofthe attendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanying drawingswhich are presented solely for illustration and not limitation of thedisclosure, and in which:

FIG. 1 illustrates an exemplary reconfigurable optical add dropmultiplexer (ROADM)-based dense wave division multiplexing (DWDM)system.

FIG. 2A illustrates an exemplary flow for detection using dark sectionconditioning (DSC).

FIG. 2B illustrates a second exemplary flow for detection using darksection conditioning (DSC).

FIG. 2C illustrates another exemplary flow for detection using darksection conditioning (DSC).

FIG. 3A illustrates an exemplary target power and gain settings for AMPsin an optical section.

FIG. 3B illustrates another exemplary target power and gain settings forAMPs in an optical section.

FIG. 4 illustrates exemplary nodal architecture with drop AMPprovisioned for demux drops.

FIG. 5 illustrates an exemplary network with channel fill and darksections.

FIG. 6 illustrates exemplary alarm and fault points for detection usingdark section conditioning (DSC).

DETAILED DESCRIPTION

Various aspects are disclosed in the following description and relateddrawings. Alternate aspects may be devised without departing from thescope of the disclosure. Additionally, well-known elements of thedisclosure will not be described in detail or will be omitted so as notto obscure the relevant details of the disclosure.

The words “exemplary” and/or “example” are used herein to mean “servingas an example, instance, or illustration.” Any aspect described hereinas “exemplary” and/or “example” is not necessarily to be construed aspreferred or advantageous over other aspects. Likewise, the term“aspects of the disclosure” does not require that all aspects of thedisclosure include the discussed feature, advantage or mode ofoperation.

Further, many aspects are described in terms of sequences of actions tobe performed by, for example, elements of a computing device. It will berecognized that various actions described herein can be performed byspecific circuits (e.g., application specific integrated circuits(ASICs)), by program instructions being executed by one or moreprocessors, or by a combination of both. Additionally, these sequence ofactions described herein can be considered to be embodied entirelywithin any form of computer readable storage medium having storedtherein a corresponding set of computer instructions that upon executionwould cause an associated processor to perform the functionalitydescribed herein. Thus, the various aspects of the disclosure may beembodied in a number of different forms, all of which have beencontemplated to be within the scope of the claimed subject matter. Inaddition, for each of the aspects described herein, the correspondingform of any such aspects may be described herein as, for example, “logicconfigured to” perform the described action.

Data communication networks may include various computers, servers,nodes, routers, switches, bridges, hubs, proxies, and other networkdevices coupled to and configured to pass data to one another. Thesedevices are referred to herein as “network elements” or “networkdevices.” Data is communicated through the data communication network bypassing protocol data units, such as Internet Protocol (IP) packets,Ethernet Frames, data cells, segments, or other logical associations ofbits/bytes of data, between the network elements by utilizing one ormore communication links between the network elements. A particularprotocol data unit may be handled by multiple network elements and crossmultiple communication links as it travels between its source and itsdestination over the network.

A “dark section” is a section wherein all the amplifier blocks in thesection remain in shutoff state due to loss of light (i.e., that notraffic carrying channels or wavelengths are present in the system).

FIG. 1 illustrates an exemplary reconfigurable optical add dropmultiplexer-based DWDM system 100 that shows an optical section or link102 that contains multiple stretched spans of optical fibers 104 a, 104b, 104 c amplified with erbium doped fiber amplifiers (EDFA) 106 a, 106b, 106 c, 106 d, 106 e, 106 f between optical add drop multiplexers(OADM) 108 a, 108 b. The number of EDFAs 106 a, 106 b, 106 c, 106 d, 106e, 106 f deployed per span 104 a, 104 b, 104 c and their target gain andpower settings can depend on the link budget requirement for thatsection. After the day 1 installation of the system, or following amaintenance window (for example fixing a fiber cut) where there is notraffic channels present, the optical section or link 102 can remaindark.

DSC can be used when a section head optical controller identifies thatthe optical section or link 102 is dark. DSC can place the first EDFA106 a in the first span 104 a in power control mode providing a lowenough power target to bring the next EDFA 106 b in the optical sectionor link 102 to come out of shutoff, and then set the rest of the EDFAs106 c, 106 d, 106 e, 106 f in the optical section or link 102 in gaincontrol mode.

Setting the first EDFA 106 a in power control mode to generate low poweramplified spontaneous emission (ASE) can serve multiple purposes. First,it can check for faults (e.g. high back reflection) on the first EDFA106 a. Second, it can generate enough power from first EDFA 106 a tokeep the span 104 a lit and perform fault detection for the next EDFA106 b in the optical section or link 102. All the other EDFAs 106 c-106f are set at a target gain that can meet the section budget requirementfor the optical section or link 102 and generate enough power to keepthe optical section or link 102 lit end-to-end. Furthermore, by keepingthe output power low at the first EDFA 106 a, the risk of damaging thefirst EDFA 106 a due to erbium concentration can be minimized in case ofan accidental optical signal flow to the first EDFA input. Since all theother EDFAs 106 b-f can run in gain control mode and their shutoffmechanism may not be disabled, they can safely shutoff as soon as thefirst EDFA 106 a goes to shutoff. Hence, the risk of damaging all theother EDFAs 106 b-f in the optical section or link 102 can be minimizedas well.

Some EDFAs have built-in back-reflector photodiodes on the output portthat can detect any amount of back-reflection coming to that port. Ifthe amount of back reflection is too high, the EDFA output power can bereduced using Automatic Power Reduction (APR). This is a safetyprocedure followed in order not to damage the EDFAs. DSC can detect APRconditions leveraging built-in measurement points that cannot beachieved via external OTDR.

FIG. 2A illustrates an exemplary flow for detection using DSC. At leastone of a broadband noise or signal can be generated at the head end ofthe section using a system available optical component that issufficient enough to turn up the next amplifier component in the section(202). Other modules in the section can operate in gain control mode(204). DSC can be implemented in various configurations. In someembodiments, the estimated power settings for the first AMP and gainsettings for the other AMPs in the section can be done in parallel. Inother embodiments, they can be done in sequence.

FIG. 2B illustrates a second exemplary flow for detection using DSC. Anautomatic shutoff mode for a first AMP in a dark section can be disabled(222). Next, the AMP can be set in a power control mode (224). Anestimated power target can be set to bring a second AMP in the sectionout of shutoff mode, wherein the second amplifier is the next amplifierin the set after the first amplifier (226). In some embodiments, asection head optical controller waits a predetermined amount of time inorder to allow the first amplifier to achieve its output power targetprior to setting all remaining amplifiers in the section in gain controlmode. All remaining AMPs in the section can be set in gain control mode(228). In some embodiments, a section head optical controller waits apredetermined amount of time in order to allow the first amplifier toachieve its output power target prior to setting all remaining AMPs inthe section in gain control mode. For example, the section head opticalcontroller can wait 5 seconds before setting all remaining AMPs.

In some embodiments, the gain for the remaining AMPs is based on thespan loss of the preceding span reported by an optical supervisorychannel. In some embodiments, the gain for the remaining AMPs is furthermodified to allow no gain changes in the event that first trafficchannels are added to the section.

FIG. 2C illustrates another exemplary flow for detection using DSC.First, a section head optical controller can begin to monitor a section(252). The condition of the section can be determined, i.e., whetherthere is an optical signal to the link (254). If the section is notdark, DSC may not be performed (256). If the section is dark, DSC may beperformed, and the section head optical controller can close all perchannel actuators at the head end OADM node (e.g. closing down thepixels in a wavelength selective switch) or moving the per channel orgroup mux variable optical attenuators to maximum attenuation) (258).Closing all per channel actuators can prevent any external signals (fromlocal mux or upstream) passing on to the section while the system willbe running DSC. To allow signals in the section while in power mode withno input may risk a Q-switch in which the available gain in theenergized erbium may all flow into the added signal and produce a highpower spike. The high power spike may flow down the line and damagevaluable optical equipment.

The section head optical controller can start conditioning the AMPs. Thesection head optical controller can disable the automatic shutoffmechanism for the first AMP in the section (e.g., by setting the shutoffthreshold for the first EDFA to −60 dBm) (260). The section head opticalcontroller can mask a safety alarm if necessary if the first AMP raisesone (262). The first AMP can be set in power control mode, and anestimated target power can be set for the AMP so that the AMP cangenerate amplified spontaneous emissions (ASEs) and maintain a constanttarget power at its output using AMP internal control loop (264).

The constant target power may be sufficient enough to bring the next AMPin the section out of shutoff. In some embodiments, the section headoptical controller can also maintain the safety of the link by keepingall safety mechanisms active.

Next, the section head optical controller can set the rest of the AMPsin gain control mode and can set gain targets for each AMP in sequence(266). It can allow a predetermined settling time (e.g., less than 5seconds) for each AMP to come out of shutoff before proceeding to nextAMP. In some embodiments, the gain for each AMP can be set based on thespan loss of the preceding span reported by optical supervisory channel(OSC). In some embodiments, the gain can be further modified or finetuned such that no gain changes would be necessary when the firsttraffic channels will be added into the dark section. The DSC can be onfor the section (268).

FIGS. 3A-3B illustrate exemplary target power and gain settings for AMPsin optical sections 300, 350 between reconfigurable OADMs 301A, 301B and351A, 351B. Target power 310, 360 can be estimated for the first AMP302, 352 and target gain can be estimated for the rest of the AMPs 304,306, 354, 356, 358 in each section 300, 350.

Target Power Calculation for First AMP (AMP Control Mode=Power)

In some embodiments, target power for the first AMP 302, 352 cancalculated as follows. The target power 310, 360 can be large enough tobring the next AMP 304, 354 in the section 300, 350 out of shutoff orloss of signal (LOS) state 312, 362. The target power 310, 360 may notbe set too low either beyond the AMP minimum output power specification,in case span loss 316, 366 is too low. The first AMP target power 310,360 may not be set at the maximum achievable target power limit and canbe kept low enough in order to avoid any possibility of damaging the AMPcircuit pack due to erbium concentration issues in case of accidentaloptical signal flow.

In some embodiments, the target power for the first AMP can be set asfollows:

Estimated_Target_Power_1st_AMP = Min[Max{Next_AMP_Input_LOS + Threshold(e.g.  3  dB) + Remote_OSC_Span_Loss, Output_LOS_1st_AMP + Threshold(e.g.  3  dB)}, Max_DSC_Power_Limit]Max_DSC_Power_Limit = Next_AMP_Shutoff_Threshold − Max_OSC_Supported_Span_LossMax_DSC_Power_Limit<< Max_Output_Power_1st_AMP

In FIGS. 3A-3B, Next_AMP_Input_LOS 312, 362 stands for the loss ofsignal threshold for the next available in the section beyond which thenext AMP 304, 354 can either shutoff or may not be able to operate inthe proper gain mask range.

Threshold 318 is defined in order to cover additional losses in the linesystem due to insertion of line interface circuit pack modules 308, ordispersion compensating components. Threshold 318 may be, for example, 3dB to cover additional losses for line interface modules and connectors.

Remote OSC_Span_Loss 320, 370 can be the span loss reported by theoptical supervisory channel (OSC) for that span 320, 370.Output_LOS_(—)1st_AMP 322, 372 can stand for the loss of signal (LOS)threshold for the 1st AMP 302, 352 output. Output_LOS_(—)1st_AMP 322,372 can also mean the minimum output power that the AMP can operatewith. Max_DSC_Power_Limit can define the maximum target power that canbe provisioned for the 1st AMP 302, 352 and is derived from the maximumspan loss supported by the optical supervisory channel, and the nextAMP's input LOS state 312, 362 (or shutoff) threshold level.

Target Gain Calculation for All the Rest of the AMPs (AMP ControlMode=Gain)

In order to calculate the target gain for all the subsequent AMPs in thesection, the target gain settings can reflect link budget for the span.For example, target gains can be further modified to set to a value thatwill be closer to a target gain settings when the first set of trafficchannels will be added to the link. If the system head opticalcontroller moves from Dark Section Conditioning (DSC) to a first set ofchannel add, minimal adjustments may be required for the AMP gainsettings that, in turn, can reduce the overall service turn up time overdark section. Such service turn up time for ‘dark’ sections can bereduced from (W+N*X) to approximately (W+1*X) where W is the wait timefor doing channel conditioning in an OADM node, N is the number ofamplifiers within that section in that direction, and X is the wait timethat needs to be allocated for each amplifier to come out of shutoff andto achieve the target gain level during dark add time frame.

For example, the target gain for the rest of the AMPs in the linesection can be estimated as below:

Estimated_Target_Gain = Max[Min_Gain, Min{Upstream_Output_Pwr − Local_Input_Pwr + Local_AMP_PerChannel_Peak_Target − Upstream_AMP_PerChannel_Peak_Target, Max_Gain}]

In some embodiments, Min_Gain and Max_Gain refer to the minimum andmaximum possible gain allowed by AMP specification or gain maskrespectively. Local_Input_Pwr can be the total input power reported onthe AMP itself where target gain is supposed to be set.Upstream_Output_Pwr can be the output power reported by the precedingAMP in the section. Some embodiments may include aLocal_AMP_PerChannel_Peak_Target, which can refer to the per channellaunch power on that AMP with 0 dB additional OSNR bias. Someembodiments can include an Upstream_AMP_PerChannel_Peak_Target, whichrefers to the per channel launch power on the preceding AMP in the linkwith 0 dB additional OSNR bias.

FIG. 4 illustrates exemplary nodal architecture of an optical add dropmultiplexer (OADM) node 400 with drop AMPs 406 provisioned for demuxdrops. The node 400 includes a pre-AMP 402 before an OADM demultiplexer(Demux) 404. The Demux 404 can send a signal to a drop AMP 406 beforechannel demux drops 408. If there are any drop AMPs 406 available beforethe channel demux drops 408 in order to cover for the demux pathinsertion losses, there will be no need to take any additional measuresfor drop AMPs 406 available before the channel demux drops 408. The dropAMPs 406 can be left in gain control mode with minimum achievable targetgain specified, and they will come out of shutoff automatically afterthe last pre-AMP 402 on the section coming out of shutoff assuming it isa broadcast and select based architecture for the node 400. A similarapproach can also be taken for a route and select based OADMarchitecture. Also shown in FIG. 4 is a channel multiplexer add 410, anOADM multiplexer 412, and a post-AMP 414.

FIG. 5 shows a typical mesh network with dark sections 502A-D availablein many segments 504A-G of the network. The proposed DSC method can beenabled in each of the dark sections 502A-D, and that should not impactany of the in-service traffic running in all other sections 504E-G. TheOADM blocks 506A-F at the ingress of each dark section 502A-D should beable to isolate or block the lights coming from upstream sections thatwill prevent damaging any AMP circuit packs running in DSC while at thesame time, any noise generated by DSC will remain confined within thedark section 502A-D, thus not disrupting traffic in downstream. As shownin FIG. 5, DSC may set a post-AMP 508A-D in power mode running atspecified target power and set all other subsequent AMPs 510A1-D3 ingain mode setting the target gain for each AMP 510A1-D3.

In some embodiments, DSC can be used with optical links with Ramanamplifiers (AMPs). Raman AMPs may not be used in isolation and aresometimes paired with a non-Raman AMP. The non-Raman AMPs can be used asthe source for the DSC mechanism. DSC can operate with Raman links aswell as proper communication links established over the Raman span sothat the section head controller can bring up the Raman AMPs out oftheir shutoff state. The controller may have to readjust the gain of theRaman pumps as part of DSC mechanism if that option is available.

DSC can be implemented remotely in multiple end-to-end connected fiberspans in parallel. The control plan can avoid enrolling traffic on afaulty link. DSC can detect a fiber cut event within an optical linkusing Automatic Laser Shutoff (ALSO), which checks for AMP shutoff andoptical supervisory channel loss of frame for that specific link.

As shown in FIG. 6, the advantages of DSC in a dark section can beexpanded beyond one section. In some embodiments, alarms and faultpoints can be detected in a non-traffic carrying dark section using DSCmechanism for a typical broadcast and select based network architecture.For example, in FIG. 6, node 602, node 604, and node 606 can bemonitored using DSC. In FIG. 6, node 602 includes a channel mux add 608,an OADM multiplexer 610, and a post-AMP 612. Node 604 includes a pre-AMP614, a variable or fixed optical attenuator (pad) or a dispersionshifted compensation module (DSCM) 616, and a post-AMP 618. Node 606includes a pre-AMP 620, an OADM demultiplexer 622, a channel demux drop624, a channel mux add 626, an OADM multiplexer 628, and a post-AMP 630.Shown in FIG. 6 is a first fiber span 632 after node 602, a second fiberspan 634 after node 604, and a third fiber span 636 after node 606. Node602 also includes a first shelf processor sectional optical controller638. Node 604 includes a second shelf processor sectional opticalcontroller 640. Node 606 includes a third shelf processor sectionaloptical controller 642.

Numerous alarm and fault points can be detected using DSC inmultiple-node configurations. For example, at a post-AMP 612 of node602, the post-AMP 612 can receive automatic power reduction (APR),shutoff, or loss of signal (LOS) for the AMPs. High back reflection onAMP-output ports can occur. Prior to the pre-AMP 614 of node 604, therecan be a line fiber cut (e.g., an Optical Line Fail), or a high receivedspan loss between inter-node adjacencies (e.g., nodes 602 and 604).There can also be an intra-node fiber disjoint, including high fiberloss (HFL) detection, between the Line Interface Modules (e.g., AMPs);Line Interface Modules to Wavelength Select Switch (WSS) (e.g., pre-AMP620 to OADM demultiplexer 622); and WSS to WSS (OADM demux 622 to OADMmultiplexer 628). A circuit pack failure of any active components in anoptical fiber can also be detected (e.g., WSS, AMP, Optical PowerMonitors, optical supervisory channels, and shelf-processors of anynode).

In some embodiments, DSC can detect the event of fiber cut within anoptical link using system-defined Automatic Line Shutoff (ALSO)technique that can check for AMP shutoff and OSC loss of frame for thatspecific link. In some cases, line AMPs can have built-in back reflectorphotodiodes on the output port that can detect any amount of backreflection coming to the port. If the amount of back reflection is toohigh, the AMP output power can be reduced, for example, with automaticpower reduction (APR). DSC can detect APR conditions leveraging built-inmeasurement points while the system is fully active, functional, andready to enroll traffic. Unlike optical time-domain reflectometer (OTDR)or external measuring equipment, DSC can be implemented without fiberdisjoint or using any external equipment.

Generally, unless stated otherwise explicitly, the phrase “logicconfigured to” as used throughout this disclosure is intended to invokean aspect that is at least partially implemented with hardware, and isnot intended to map to software-only implementations that areindependent of hardware. Also, it will be appreciated that theconfigured logic or “logic configured to” in the various blocks are notlimited to specific logic gates or elements, but generally refer to theability to perform the functionality described herein (either viahardware or a combination of hardware and software). Thus, theconfigured logics or “logic configured to” as illustrated in the variousblocks are not necessarily implemented as logic gates or logic elementsdespite sharing the word “logic.” Other interactions or cooperationbetween the logic in the various blocks will become clear to one ofordinary skill in the art from a review of the aspects described belowin more detail.

Those of skill in the art will appreciate that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Further, those of skill in the art will appreciate that the variousillustrative logical blocks, modules, circuits, and algorithm stepsdescribed in connection with the aspects disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the aspects disclosed herein may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The methods, sequences and/or algorithms described in connection withthe aspects disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM, flash memory, ROM, EPROM, EEPROM,registers, hard disk, a removable disk, a CD-ROM, or any other form ofstorage medium known in the art. An exemplary storage medium is coupledto the processor such that the processor can read information from, andwrite information to, the storage medium. In the alternative, thestorage medium may be integral to the processor. The processor and thestorage medium may reside in an ASIC. The ASIC may reside in a userterminal (e.g., UE). In the alternative, the processor and the storagemedium may reside as discrete components in a user terminal.

In one or more exemplary aspects, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by acomputer. By way of example, and not limitation, such computer-readablemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother medium that can be used to carry or store desired program code inthe form of instructions or data structures and that can be accessed bya computer. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

While the foregoing disclosure shows illustrative aspects of thedisclosure, it should be noted that various changes and modificationscould be made herein without departing from the scope of the disclosureas defined by the appended claims. The functions, steps and/or actionsof the method claims in accordance with the aspects of the disclosuredescribed herein need not be performed in any particular order.Furthermore, although elements of the disclosure may be described orclaimed in the singular, the plural is contemplated unless limitation tothe singular is explicitly stated.

What is claimed is:
 1. A method for optical dark section conditioning,comprising: responsive to determining that a section is dark, wherein adark section comprises connected fiber spans that are functional with notraffic carrying channels present, generating at least one of abroadband noise and a signal at a head end of the section, by a firstmodule of the section; and operating all other modules of the section ingain control mode.
 2. The method of claim 1, further comprising closingall per channel actuators at a head end optical add drop multiplexer(OADM) node.
 3. The method of claim 2, further comprising closing downpixels in a wavelength selective switch.
 4. The method of claim 2,further comprising changing a per channel or a group multiplexervariable optical attenuator to an approximate maximum attenuation. 5.The method of claim 1, further comprising masking an alarm raised by afirst amplifier at the head of the section.
 6. The method of claim 1,wherein the target gain for the other modules is based on a span loss ofa preceding span, as determined by an optical supervisory channel. 7.The method of claim 1, wherein the gain for the other modules issubstantially based on prior results.
 8. The method of claim 1, furthercomprising setting gain targets for all modules in gain control mode. 9.The method of claim 1, wherein a section head optical controller waits apredetermined amount of time in order to allow a first amplifier toachieve its output power target prior to setting the other modules inthe section in gain control mode.
 10. An apparatus for optical darksection conditioning, comprising: logic configured to, responsive to adetermination that a section is dark, wherein a dark section comprisesconnected fiber spans that are functional with no traffic carryingchannels present, generate at least one of a broadband noise and asignal at a head end of the section by a first module of the section;and logic configured to operate all other modules of the section in gaincontrol mode.
 11. The apparatus of claim 10, further comprising logicconfigured to close all per channel actuators at a head end optical adddrop multiplexer node.
 12. The apparatus of claim 11, further comprisinglogic configured to close down pixels in a wavelength selective switch.13. The apparatus of claim 11, further comprising logic configured tochange a per channel or a group multiplexer variable optical attenuatorto an approximate maximum attenuation.
 14. The apparatus of claim 10,further comprising logic configured to mask an alarm raised by the firstamplifier.
 15. The apparatus of claim 10, wherein the target gain forthe other modules is based on a span loss of a preceding span reportedby an optical supervisory channel.
 16. The apparatus of claim 10,wherein the gain for the other modules is substantially based on priorresults.
 17. The apparatus of claim 10, further comprising logicconfigured to set gain targets for all modules in gain control mode. 18.The apparatus of claim 10, wherein the section head optical controllerwaits a predetermined amount of time in order to allow a first amplifierto achieve its output power target prior to setting all other modules inthe section in gain control mode.
 19. An apparatus for optical darksection conditioning, comprising: a processor configured to responsiveto a determination that a section is dark, wherein a dark sectioncomprises connected fiber spans that are functional with no trafficcarrying channels present, generate at least one of a broadband noiseand a signal at a head end of the section by a first module of thesection; and cause all other modules of the section to operate in gaincontrol mode.
 20. The apparatus of claim 19, wherein the processor isconfigured to perform optical dark section conditioning on more than onedark section.
 21. The apparatus of claim 20, wherein the more than onedark section comprises at least one of the following: a route and selectbased network architecture and a broadcast and select-basedarchitecture.
 22. The apparatus of claim 20, wherein the processor isconfigured to perform optical dark section conditioning on a sectionthat comprises at least one Raman amplifier.
 23. The apparatus of claim19, wherein at least one of the modules has a back-reflector photodiodeon an output port to detect back-reflection coming into the port. 24.The apparatus of claim 19, wherein the processor is configured to reduceoutput power in order not to damage the modules.
 25. A non-transitorycomputer-readable medium storing instructions executable by a processorfor optical dark section conditioning, comprising: at least oneinstruction to generate, responsive to a determination that a section isdark, wherein a dark section comprises connected fiber spans that arefunctional with no traffic carrying channels present, at least one of abroadband noise and a signal at a head end of the section by a firstmodule of the section; and at least one instruction to operate all othermodules of the section in gain control mode.
 26. The apparatusnon-transitory computer-readable medium of claim 25, further comprisingat least one instruction to perform optical dark section conditioning onmore than one dark section.
 27. The non-transitory computer-readablemedium of claim 25, wherein the more than one dark section comprises atleast one of the following: a route and select based networkarchitecture and a broadcast and select-based architecture.
 28. Thenon-transitory computer-readable medium of claim 25, performs furthercomprising at least one instruction to perform optical dark sectionconditioning on a section that comprises at least one Raman amplifier.29. The non-transitory computer-readable medium of claim 25, wherein atleast one of the modules has a back-reflector photodiode on an outputport to detect back-reflection coming into the port.
 30. Thenon-transitory computer-readable medium of claim 25, further comprisingat least one instruction to reduce output power in order not to damagethe modules.
 31. A method for optical dark section conditioning,comprising: disabling an automatic shutoff mode for a first amplifier ina dark section comprising connected fiber spans that are functional withno traffic carrying channels present; setting the first amplifier inpower control mode; setting an estimated power target to bring a secondamplifier in the section out of shutoff mode, wherein the secondamplifier is the next amplifier in the set after the first amplifier;and setting all remaining amplifiers in the section in gain controlmode.
 32. The method of claim 1, further comprising detecting a fault inthe section while the section is dark based on the optical dark sectionconditioning.
 33. The apparatus of claim 10, further comprising logicconfigured to detect a fault in the section while the section is darkbased on the optical dark section conditioning.